Via the Daily Beast:

For the past few days, a mystery has been unfolding in Silicon Valley. Somebody, it seems, hired Burson-Marsteller, a top public-relations firm, to pitch anti-Google stories to newspapers, urging them to investigate claims that Google was invading people’s privacy. Burson even offered to help an influential blogger write a Google-bashing op-ed, which it promised it could place in outlets like The Washington Post, Politico, and The Huffington Post.
The plot backfired when the blogger turned down Burson’s offer and posted the emails that Burson had sent him. It got worse when USA Today broke a story accusing Burson of spreading a “whisper campaign” about Google “on behalf of an unnamed client.”
But who was the mysterious unnamed client? While fingers pointed at Apple and Microsoft, The Daily Beast discovered that it’s a company nobody suspected—Facebook.

It appears that the social-media giant hired the PR firm Burson-Marsteller because it didn’t like Google using Facebook users’ data for their own social-networking service.